A current measurement method based on an optical fiber current sensor

Abstract

The application discloses a current measurement method based on an optical fiber current sensor and belongs to the field of optical fiber sensing. The period of a basic digital square wave is composed of a current signal collection period and a vibration signal collection period, and the size is related to the round-trip time of the modulated light. The current phase shift and the vibration phase shift are collected in the two collection periods respectively, the first digital step wave and the second digital step wave are obtained according to the two phase shifts, the total phase of the optical fiber current sensor is kept at the sensitive point of pi / 2 in the current signal collection period through the reset and closed-loop modulation functions, the total phase of the optical fiber current sensor is kept at the insensitive point of 0 in the vibration signal collection period, the current signal and the vibration signal are obtained, the time of vibration occurrence is determined through the vibration signal, and the vibration filtering is performed on the current signal. The method can improve the measurement precision and stability and avoid the occurrence of false locking accidents.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber sensing, and more particularly relates to a current measurement method based on an optical fiber current sensor. BACKGROUND

[0002] The optical fiber current sensor has obvious advantages in the application in the extra-high voltage power grid due to its good insulation performance, wide frequency band, strong anti-electromagnetic interference ability, large dynamic range, small size and light weight. The optical fiber current sensor is one of the key devices of the high-voltage direct-current converter station, which measures the high-voltage direct-current transmission current and transmits the measurement result to the direct-current control and protection device. The various performances of the optical fiber current sensor itself have a great relationship with the stable operation of the converter station and even the stability of the direct-current transmission system. However, some failures have occurred in actual engineering applications, in which the measurement failure caused by vibration leads to the direct-current lockout or outage accident.

[0003] In the measurement process of the optical fiber current sensor based on the Faraday optical rotation effect, the existence of linear birefringence will cause the measurement error to increase. The optical fiber is an elastic object, and when the vibration propagates in the optical fiber, it will cause the vibration of the internal particles of the optical fiber, and will also transmit energy to the particles at the adjacent position, so that the particles at the adjacent position also start to vibrate, and the wave phenomenon is generated. The vibration changes the linear birefringence of the sensing optical fiber, which will cause the polarization state of the light wave propagating in the sensing optical fiber to change. If only the vibration signal is roughly regarded as a high-frequency signal and the current is regarded as a low-frequency signal, and the vibration signal is filtered out through a low-pass filter, the meaningful high-frequency current signal (the upper limit of the frequency is the modulation frequency) will also be inevitably filtered out, which will reduce the bandwidth of the current sensor and affect the measurement accuracy of the optical fiber current sensor. In the current engineering application, only the traditional modulation scheme of the current closed-loop feedback is used, and it is difficult to distinguish whether the signal is vibration or current generated in the face of vibration interference, which will lead to the mislock accident. SUMMARY

[0004] In view of the above defects or improvement needs of the prior art, the present application provides a current measurement method based on an optical fiber current sensor, which can measure the current and vibration signal at the same time, so as to accurately filter out the influence of vibration and improve the current measurement accuracy.

[0005] To achieve the above purpose, according to the first aspect of the present application, a current measurement method based on an optical fiber current sensor is provided, which comprises:

[0006] S1, constructing a basic digital square wave V base ; wherein V baseThe cycle length is τ, and 0~τ / 4 and τ / 2~3τ / 4 are used as the current signal acquisition period, and the corresponding square wave amplitudes are π / 2 and 0 respectively. τ / 4~τ / 2 and 3τ / 4~τ are used as the vibration signal acquisition period, and the corresponding square wave amplitudes are all 0;

[0007] S2, V base Load it into the phase modulator, pass the current to be measured into the wire, and calculate the phase difference of the signal collected by the photodetector at 0~τ / 4 and τ / 2~3τ / 4 respectively And the phase difference of the signals collected at τ / 4~τ / 2 and 3τ / 4~τ And according to Construct the first and second digital step waves V with a period of τ step_1 、V step_2 ; Among them, V step_1 Step height V step_2 Step height n1, n2 are gain coefficients;

[0008] S3, V step_1 、V step_2 Superimposed on V base Get the modulated signal and load it into the phase modulator, so that the phase modulator generates The first feedback phase and the second feedback phase are mutually opposite, so that the modulation phase of the optical fiber current sensor in the current signal acquisition period and the vibration signal acquisition period always remains at π / 2 and 0 respectively within the current cycle τ, so that the optical fiber current sensor operates at the most sensitive point and the least sensitive point of current measurement in the current signal acquisition period and the vibration signal acquisition period respectively; save ΔV1 and ΔV2 corresponding to the current cycle τ, set τ=τ+1, and return to S2;

[0009] S4, performing modal decomposition on ΔV1 and ΔV2 corresponding to each period τ to obtain a target signal and a vibration signal; obtaining the vibration occurrence time according to the vibration signal, performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measurement value of the current to be measured.

[0010] According to a second aspect of the present invention, there is provided an electronic device comprising: a computer-readable storage medium and a processor;

[0011] The computer-readable storage medium is used to store executable instructions;

[0012] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method according to the first aspect.

[0013] According to a third aspect of the present application, a computer readable storage medium is provided, which stores computer instructions for causing a processor to perform the method according to the first aspect.

[0014] According to a fourth aspect of the present application, a computer program product is provided, which comprises computer programs or instructions, which, when executed by a processor, implement the method according to the first aspect.

[0015] In general, the above technical solutions conceived by the present application can achieve the following beneficial effects compared with the prior art:

[0016] The method provided by the present application sets the period of the basic digital square wave, which is composed of a current signal acquisition period and a vibration signal acquisition period, and the size is related to the round-trip time of the modulated light. The current phase shift and the vibration phase shift are acquired in the two acquisition periods respectively, the first digital step wave and the second digital step wave are obtained according to the two phase shifts, and the reset and closed-loop modulation functions are used to keep the total phase of the fiber current sensor at the sensitive point of π / 2 in the current signal acquisition period and keep the total phase of the fiber current sensor at the insensitive point of 0 in the vibration signal acquisition period. The current signal and the vibration signal are obtained, the time of vibration occurrence is determined through the vibration signal, the vibration filtered current signal is obtained by performing vibration filtering on the current signal, and the measurement value of the to-be-measured current is obtained. The method provided by the present application can realize the simultaneous measurement of the current and the vibration, accurately filter the vibration, improve the measurement precision and stability, accurately distinguish the vibration signal when the vibration interference occurs, and avoid the occurrence of false locking accidents. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is a flowchart of a current measurement method based on a fiber current sensor provided by an embodiment of the present application;

[0018] Figure 2 FIG. 2 is a structural diagram of a reflective fiber current transformer;

[0019] Figure 3 FIG. 3 is an output corresponding diagram of the fiber current sensor when a current is loaded;

[0020] Figure 4 FIG. 4 is a modulation phase change diagram provided by an embodiment of the present application;

[0021] Figure 5 FIG. 5 is a step wave reset diagram provided by an embodiment of the present application;

[0022] Figure 6 FIG. 6 is a digital signal waveform diagram of the current and the vibration provided by an embodiment of the present application;

[0023] Figure 7 is a waveform diagram of the current mode decomposed data group and the vibration mode decomposed data group provided by the embodiment of the present application;

[0024] Figure 8 is a waveform diagram of the digital signal of the current before and after vibration filtering provided by the embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0026] The embodiment of the present application provides a current measurement method based on an optical fiber current sensor, as shown in Figure 1 , the method comprises:

[0027] S1, constructing a basic digital square wave V base ; wherein the period length of V base is τ, 0~τ / 4 and τ / 2~3τ / 4 are taken as current signal collection periods, and the corresponding square wave amplitudes are π / 2 and 0, respectively, τ / 4~τ / 2 and 3τ / 4~τ are taken as vibration signal collection periods, and the corresponding square wave amplitudes are both 0.

[0028] The method provided by the embodiment of the present application is suitable for a reflective or transmissive optical fiber current sensor, wherein if the optical fiber current sensor is a reflective optical fiber current sensor, τ=2t`, and if the optical fiber current sensor is a transmissive optical fiber current sensor, τ=t`, t` is a modulation light round-trip time.

[0029] The following will be described taking a reflective optical fiber current sensor as an example.

[0030] The structure of the reflective optical fiber current sensor is as shown in Figure 2 . The modulation light round-trip time t` is the time required for the light to travel from the phase modulator to the mirror and then return to the phase modulator, which is measured according to the optical fiber current sensor optical path length; the duration of one period of the basic digital square wave τ=2t`.

[0031] The duration of one period of the basic digital square wave V base is τ, the duration of the current signal collection period is 0~τ / 4 and τ / 2~3τ / 4, which is indicated by a triangle in Figure 3 , and the duration of the vibration collection period is τ / 4~τ / 2 and 3τ / 4~τ, which is indicated by a circle in Figure 3 ;

[0032] Set the V at 0 to τ / 4 in the current signal acquisition cycle base The amplitude is the half-wave voltage of the phase modulator (the corresponding modulation phase is π / 2), and the V base The amplitude is 0; set V at τ / 4 to τ / 2 in the vibration signal acquisition period base The amplitude is 0, and V at 3τ / 4~τ in the vibration signal acquisition period base The amplitude is 0; the phase change during round-trip modulation and the total modulation phase are as follows Figure 4 As shown. It can be understood that when the circularly polarized light is reflected by the reflector, the left-handed circularly polarized light is converted into right-handed polarized light, and at the same time, the right-handed circularly polarized light is converted into left-handed polarized light. After passing through the quarter-wave plate, the polarization plane of the linearly polarized light undergoes x-axis and y-axis swapping, resulting in a phase difference between the two beams before and after passing through the phase modulator, which is

[0033] S2, V base Load it into the phase modulator, pass the current to be measured into the wire, and calculate the phase difference of the signal collected by the photodetector at 0~τ / 4 and τ / 2~3τ / 4 respectively And the phase difference of the signals collected at τ / 4~τ / 2 and 3τ / 4~τ And according to Construct the first and second digital step waves V with a period of τ step_1 、V step_2 ; Among them, V step_1 Step height V step_2 Step height n1, n2 are gain coefficients;

[0034] Specifically, and Also called first phase shift and second phase shift.

[0035] In step S2, V base After loading it into the phase modulator and passing the current to be measured into the wire, first, the difference between the signal of 0 to τ / 4 in the current signal acquisition period obtained by the photodetector signal and the signal of τ / 2 to 3τ / 4 in the current signal acquisition period obtained by the photodetector signal is calculated as the first phase shift The difference between the signal of τ / 4 to τ / 2 in the vibration signal acquisition period obtained by the photodetector signal and the signal of 3τ / 4 to τ in the vibration signal acquisition period obtained by the photodetector signal is the second phase shift

[0036] like Figure 3As shown in the figure, when the circularly polarized light in the sensing ring of the fiber optic current sensor is affected by birefringence, including the circular birefringence generated when the current flows through the conductor and the linear birefringence generated by the knocking vibration, both will cause the left-handed circularly polarized light and the right-handed circularly polarized light to generate a phase difference.

[0037] Since the total modulation phase of the fiber optic current sensor during the current signal acquisition period is π / 2, the fiber optic current sensor operates at the most sensitive point and can measure the circular birefringence generated when current flows through the conductor and the linear birefringence generated by the knocking vibration;

[0038] Since the total modulation phase of the fiber optic current sensor during the vibration signal acquisition period is 0, the fiber optic current sensor operates at the least sensitive point and can only measure the linear birefringence and loss changes caused by the knocking vibration, but is not affected by the circular birefringence generated when the current flows through the conductor, thereby realizing the measurement of the vibration signal.

[0039] Then, in step S2, a first digital step wave that can be automatically reset and has a step height corresponding to a first feedback phase is generated within the current signal acquisition period based on the first phase shift; a second digital step wave that can be automatically reset and has a step height corresponding to a second feedback phase is generated within the vibration signal acquisition time based on the second phase shift; the first digital step wave and the second digital step wave are superimposed on the basic digital square wave to obtain a digital modulated signal.

[0040] Specifically, let the digital step wave be V step , the modulation voltage after the digital step wave is superimposed on the basic digital square wave is V modulation , the full-wave voltage of the phase modulator is V π , the positive overflow modulation voltage is V over_p , the negative overflow modulation voltage is V over_n ;

[0041] In the digital logic circuit, set the first digital step wave V step_1 , the step height is The second digital step wave V step_2 , the step height Among them, n1 and n2 are gain coefficients, which can be set by yourself;

[0042] Determine the modulation voltage V modulation =V base +V step_1 +V step_2 In the overflow situation, when V modulation >V π , the positive overflow modulation voltage is V over_p =V modulation -V π , when Vmodulation <-V π , the negative overflow modulation voltage is V over_n =V modulation +V π ; Among them, it can be understood that since the fiber optic current sensor can measure currents of different polarities, there is also and Accordingly, when the modulation voltage V modulation <-V π There will be a negative overflow situation;

[0043] When positive overflow occurs, V modulation =V over_p , when negative overflow occurs, the V modulation =V over_n , in order to achieve automatic reset;

[0044] The calculation method of the first digital step wave and the second digital step wave of automatic reset is the same, such as Figure 5 shown.

[0045] S3, V step_1 、V step_2 Superimposed on V base Get the modulated signal and load it into the phase modulator, so that the phase modulator generates The first feedback phase and the second feedback phase are opposite to each other, so that the modulation phase of the optical fiber current sensor in the current signal acquisition period and the vibration signal acquisition period is always maintained at π / 2 and 0 respectively within the current period τ, so that the optical fiber current sensor works at the most sensitive point and the least sensitive point of current measurement in the current signal acquisition period and the vibration signal acquisition period respectively; save ΔV1 and ΔV2 corresponding to the current period τ, set τ=τ+1, and return to S2.

[0046] Specifically, within a current signal acquisition cycle, the total modulation phase of the fiber optic current sensor is controlled by a first feedback phase and a first phase shift. To keep the fiber optic current sensor operating at its most sensitive point to measure the current signal, the first feedback phase is adjusted within each current signal acquisition cycle. The first feedback phase and the first phase shift are equal in magnitude and opposite in sign, thereby maintaining the total modulation phase of the fiber optic current sensor at π / 2, thereby achieving closed-loop modulation of the fiber optic current sensor.

[0047] During the vibration signal acquisition cycle, the total modulation phase of the fiber optic current sensor is controlled by the second feedback phase and the second phase shift. In order to keep the fiber optic current sensor operating at the least sensitive point to measure the vibration signal while avoiding the influence of the current signal, the second feedback phase is adjusted during each vibration signal acquisition cycle. The second feedback phase is equal to the second phase shift in magnitude but opposite in sign, thereby keeping the total modulation phase of the fiber optic current sensor at 0, thereby realizing closed-loop modulation of the fiber optic current sensor.

[0048] At the same time, the first feedback phase is stored in the current signal acquisition period to obtain a digital signal of current; and the second feedback phase is stored in the vibration signal acquisition period to obtain a digital signal of vibration.

[0049] That is, in step S3, the digital modulation signal is applied to the phase modulator after passing through the digital-to-analog converter to generate a first feedback phase and a second feedback phase; wherein the first feedback phase is equal to the first phase shift in magnitude and opposite in sign, so that the total modulation phase of the optical fiber current sensor during the current signal acquisition period is π / 2; the second feedback phase is equal to the second phase shift in magnitude and opposite in sign, so that the total modulation phase of the optical fiber current sensor during the vibration signal acquisition period is 0; thereby realizing the normal reset and closed-loop modulation of the optical fiber current sensor.

[0050] After the current cycle τ ends, the next cycle is entered, that is, τ=τ+1, and the process returns to step S2 until all cycles are traversed.

[0051] S4, performing modal decomposition on ΔV1 and ΔV2 corresponding to each period τ to obtain a target signal and a vibration signal; obtaining the vibration occurrence time according to the vibration signal, performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measurement value of the current to be measured.

[0052] Specifically, the modulation amount ΔV1 for generating the first feedback phase is stored in the current signal acquisition cycle. It is a dimensionless number. Since the first feedback phase Δw1 is different from the first phase shift Related, And the first phase shift Including the phase shift caused by the current to be measured and the phase shift caused by vibration, according to The magnitude of the current to be measured can be calculated; similarly, the modulation amount ΔV2 for generating the second feedback phase is stored during the vibration signal acquisition period. Accordingly, Includes phase shifts caused by vibrations.

[0053] In order to more clearly show the effect of the vibration generated by tapping the sensor ring on the current signal and the vibration signal, Figure 6It can be found that the signal ΔV1 collected in the current signal acquisition period includes current signal and vibration signal, but the time of vibration occurrence cannot be intuitively distinguished from the time domain; at the same time, the signal ΔV2 collected in the vibration signal acquisition period also cannot intuitively distinguish the time of vibration occurrence from the time domain, so modal decomposition processing is needed:

[0054] The signal ΔV1 collected in the current signal acquisition period is subjected to modal decomposition processing to obtain a current modal decomposition data set, which includes current and vibration signals, that is, the target signal obtained by modal decomposition processing of ΔV1 includes current signal and vibration signal; the signal ΔV2 collected in the vibration signal acquisition period is subjected to modal decomposition processing to obtain a vibration modal decomposition data set, which only includes vibration signal; by comparing the current modal decomposition set and the vibration modal decomposition set, the time of vibration occurrence is determined, and the current signal corresponding to the time point is subjected to vibration filtering to separate out the current signal, which represents the phase shift caused by the current According to the formula The size of the current to be measured is obtained, wherein N is the number of sensing optical fiber winding turns, V is the Wiedemann constant, which is related to the material properties; I is the size of the current to be measured, that is, the measured value.

[0055] In order to more clearly show the recognition ability of the knock modal decomposition processing for the time of vibration occurrence, combined with Figure 7 It can be found that the vibration in the current modal decomposition data set and the vibration modal decomposition data set is in the same position, the time of vibration occurrence is successfully analyzed, the vibration interference in the current signal can be accurately filtered out, and the comparison of the current signal before and after vibration filtering is as shown in Figure 8 In the system of the optical fiber current sensor of the embodiment, the actual current signal acquisition period and the vibration signal acquisition period are both 3.976 μs, and the sampling rate is 251.5 kSa / s.

[0056] The method used for modal decomposition is one of EMD, EEMD, CEEMDAN and VMD.

[0057] In summary, the method provided by the embodiment of the application realizes double-sensitivity measurement by decomposing the period tau of a basic digital square wave of an existing optical fiber current sensor into two parts and performing closed-loop feedback modulation according to corresponding phase shifts, respectively, because the total phase of the two parts is different; the total phase of the optical fiber current sensor is kept at a sensitive point of pi / 2 in a current signal acquisition period, so that the current sensitivity is maximum, the total phase of the optical fiber current sensor is kept at an insensitive point of 0 in a vibration signal acquisition period, so that the current sensitivity is minimum, when vibration occurs, the current signal and the vibration signal are included in the data in the current signal acquisition period, but only the vibration signal is included in the data in the vibration signal acquisition period; the time when the vibration occurs is determined according to the vibration signal, and vibration filtering of the current digital signal is realized purposefully.

[0058] The embodiment of the application provides an electronic device, comprising: a computer readable storage medium and a processor.

[0059] The computer readable storage medium is used for storing executable instructions.

[0060] The processor is used for reading the executable instructions stored in the computer readable storage medium, and performing the method as described in the above embodiment.

[0061] The embodiment of the application provides a computer readable storage medium, and the computer readable storage medium stores computer instructions, and the computer instructions are used for making a processor execute the method as described in the above embodiment.

[0062] The embodiment of the application provides a computer program product, comprising a computer program or instructions, and the computer program or instructions are executed by a processor to realize the method as described in the above embodiment.

[0063] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the application, and is not used to limit the application, and any modification, equivalent replacement and improvement made within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A current measurement method based on an optical fiber current sensor, characterized in that: The method comprises: S1, build basic digital square wave ;in, The cycle length is ,Will and As the current signal acquisition period, the corresponding square wave amplitudes are π / 2 and 0 respectively. and As the vibration signal acquisition period, the corresponding square wave amplitude is 0; S2, will Load it into the phase modulator, pass the current to be measured into the wire, and calculate the photodetector's and Phase difference of the collected signal , and respectively and Phase difference of the collected signal , and according to 、 The construction cycle duration is The first and second digital step waves 、 ;in, Step height , Step height , , is the gain coefficient; S3, will 、 Overlay to Get the modulated signal and load it into the phase modulator, so that the phase modulator generates 、 The first feedback phase and the second feedback phase are mutually opposite, so that the modulation phase of the optical fiber current sensor in the current signal acquisition cycle and the vibration signal acquisition cycle is in the current cycle. The values ​​are always kept as π / 2 and 0 respectively, so that the optical fiber current sensor works at the most sensitive point and the least sensitive point of current measurement during the current signal acquisition cycle and the vibration signal acquisition cycle respectively; the current cycle is saved. Corresponding and ,make = +1, return to S2; S4, for each cycle Corresponding and Performing modal decomposition to obtain a target signal and a vibration signal; obtaining a vibration occurrence time according to the vibration signal, performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measured value of the current to be measured; Before step S4, it also includes: judging the current cycle Modulation voltage Is it greater than or less than ,like , then let the period ,like , then let the period ;in, , , is the full-wave voltage of the phase modulator; If the fiber optic current sensor is a reflective fiber optic current sensor, then If the fiber optic current sensor is a transmission fiber optic current sensor, , is the round-trip transit time of the modulated light.

2. The method according to claim 1, wherein In step S4, according to the formula Calculate the measured value of the current to be measured I ;in, is the current signal, N is the number of windings of the sensing optical fiber, V is the Weddell constant.

3. An electronic device, characterized in that: include: Computer-readable storage medium and processor; The computer-readable storage medium is used to store executable instructions; The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method according to claim 1 or 2.

4. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to claim 1 or 2.

5. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the method according to claim 1 or 2 is implemented.

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